The present invention relates to a method and an apparatus for the automatic control of a blood centrifuge.
The hematocrit value is the percentage of the volume of the blood that is occupied by red blood cells. During some medical procedures, such as, for example, autotransfusion during or after surgery, there is a need to increase the blood""s hematocrit value. Increasing the blood""s hematocrit value is currently performed in blood centrifuges where blood is introduced by a peristaltic pump.
A blood centrifuge substantially comprises two coaxial and rigidly coupled bell-shaped chambers arranged with one inside the other. The portion of space between the two chambers defines a cell that receives the blood. The cell is connected to the outside by an inlet tube and a discharge tube. The inlet tube and discharge tube are connected to the bell-shaped chambers by a rotary coupling. The blood centrifuge rotates the chambers about their axis while the tubes are kept motionless.
The centrifugation procedure entails a first step of filling the cell. The cell is filled by introducing blood through the inlet tube. The centrifugal force propels the blood away from the rotational axis. The blood centrifuge packs the red blood cells in the cell against the wall of the outer chamber. The red blood cells pack against the outer wall because they are more dense than the blood""s other components. Other cellular components, such as white blood cells and platelets, are arranged in a thin layer known as buffy coat directly adjacent to the mass of packed red cells. The buffy coat assumes an orientation substantially parallel to the centrifuge""s rotational axis. The separated plasma, the remaining component of blood, is arranged in a layer which lies above the buffy coat closer to the rotation axis. As filling continues, the buffy coat moves closer to the rotation axis displacing the separated plasma toward the discharge tube. When the plasma reaches the discharge tube the plasma flows out of the cell into an adapted collection bag. The outgoing flow of plasma continues until an optical sensor detects that the buffy coat has reached the discharge tube indicating the centrifuge is full. When the buffy coat reaches the discharge tube the filling step is complete. No additional blood is introduced into the centrifuge. The centrifuge now contains almost exclusively packed red cells and the buffy coat, since the separated plasma has been almost completely displaced from the cell.
Optionally, the filling step is followed by a washing step for the red blood cells and by an emptying step during which the cells are collected in a suitable bag. In any case, the invention relates to the filling step because the hematocrit value of the blood after filling remains substantially unchanged during the subsequent steps.
After the filling step, the hematocrit value of the collected blood is higher than the hematocrit value of the input blood. The hematocrit value of the collected blood varies with each centrifugation. The collected blood""s hematocrit value depends on the trend of the input blood""s hematocrit value over time, which is normally variable, and the flow rate of blood into the cell. For example, a low flow rate allows a high degree of packing of the red cells, with a high hematocrit value, but entails a long filling time which is sometimes incompatible with emergency conditions; or, alternatively, a high flow rate reduces the procedure time but the collected blood""s hematocrit value is typically only slightly higher than the input blood""s hematocrit value.
The flow rate of input blood is the only directly controllable variable for blood centrifugation during the filling step. Therefore, the flow rate is altered to adapt the collected blood to specific requirements. There is currently no system for automatically controlling the operation of a blood centrifuge. An operator typically controls the flow rate by adjusting the pump based on experience. The operator determines how the flow rate should be adjusted by continuously monitoring the centrifugation or by choosing among a certain number of predefined procedures, but these techniques have drawbacks. The drawbacks can include an inaccuracy in the result and considerable direct involvement of the operator. In any case, final hematocrit value and the time for centrifugation have never been predictable.
The aim of the present invention is to provide an apparatus and a method for the automatic control of a blood centrifuge. More particularly, the present invention provides a system for controlling the flow rate of the blood fed into the centrifuge. The system is capable of obtaining a specific hematocrit value for the collected blood with a forecast of the time required for the centrifugation procedure. Alternatively, the system is capable of ensuring completion of the operation in a very specific time with a forecast of the hematocrit value collected blood at the end of the procedure.
In one aspect, this invention is a method for the automatic control of a blood centrifuge wherein blood is added to the centrifuge in a filling step and red blood cells are separated from the blood in a settling process the method comprising providing a blood centrifuge, a blood pump for communicating blood to the centrifuge and a controller configured to receive data and to produce at least one output; providing first input data to the controller indicative of a selected output parameter comprising one of a desired hematocrit value for blood after completion of the filling step and a desired time required to complete the filling step; providing second input data to the controller indicative of a hematocrit value of blood entering the blood centrifuge; providing third input data indicative of a level of packed red blood cells in the blood centrifuge to the controller; providing fourth input data to the controller indicative of a volume of red blood cells in the centrifuge; and processing the first, second, third and fourth input data in the controller to produce a first output for controlling blood flow rate through the pump during the filling step.
The first, second, third and fourth input data in the controller may be processed to produce a second output comprising one of an output indicative of time required for completion of the filling step, if the first input data is a desired hematocrit value for blood after the filling step, and an output indicative of the hematocrit value at the end of the filling step, if the first input data is a desired time for completing the filling step.
The controller may process the input data using a neural network, or by using experimentally obtained input data and output parameters. In addition, the controller may process the input data using both the input data and the output parameters that govern the settling process, or it may process the input data based on analytic or numerical solution of the input data and output parameters that govern the settling process. The controller may also process the input data using a generic mathematical function, optimized for the purpose experimentally or optimized on the basis of input data and output parameters governing the settling process.
The third input data indicative of the level of packed red blood cells may be provided by a buffy coat level sensor. The second input data indicative of a hematocrit may be provided by a hematocrit sensor.
The third input data for the level of packed red blood cells may be calculated using an algorithm based on the flow rate of a pump providing input blood to the centrifuge and the hematocrit value of the input blood.
The fourth input data to the controller indicating the volume of red blood cells in the centrifuge may be provided by a processing unit.
In another aspect, this invention is an apparatus for the automatic control of a blood centrifuge wherein blood is added to the centrifuge in a filling step and red blood cells are separated from the blood in a settling process, the apparatus comprising a blood pump communicating blood to the centrifuge; a first sensor configured to measure a hematocrit value of blood entering the blood centrifuge and produce data indicative of the hematocrit value; a second sensor configured to measure a level of packed red blood cells during centrifugation and produce data indicative of the level of packed red blood cells; a processing unit for producing data indicative of a volume of red blood cells in the centrifuge; an operator interface for producing data indicative of a selected output parameter comprising one of a desired hematocrit value for blood after completion of the filling step and a desired time required to complete the filling step; and a controller configured to receive the data from the first and second sensors, the processing unit and the operator interface, in order to produce a first output for controlling blood flow rate to achieve the selected output parameter. The controller may be further configured to produce a second output comprising one of an output indicative of time required for completion of the filling step, if the selected parameter of the first input data is a desired hematocrit value for blood after the filling step, and an output indicative of the hematocrit value at the end of the filling step, if the selected parameter of the first input data is a desired time for completing the filling step. The controller may be further configured to receive data indicative of a flow rate of blood and a volume of red blood cells.
Further characteristics and advantages of the present invention will become apparent from the following detailed description as illustrated in the accompanying drawings.